However,
Khare and Sukhatme [1]}, [2]} have pointed out another type of degeneracy which
is not obtained by using expansions in series of hypergeometric functions. In fact, this type of
degenerate solutions comes from expansions in
series of \(\mathrm {cn}^2u\)  or \(\mathrm {sn}^2u\) 
for particular values for \(\mathbf {l}\)  and \(\mathbf {m}\) ,
as explained in Appendix C.
